This invention relates generally to time displays for electronic timepieces and particularly to electro-optical displays showing the time in analog or conventional type form.
Mechanical watches and clocks have long used hour and minute hands to show the time, and nearly everyone is intimately familar with such displays. The hour and minute hands not only show the time but also provide the user with a graphic picture of how long it is until some future even time. Most electronic watches presently on the market have decimal digit read outs which show the time precisely in numbers. The user needs only to read the number to "tell" the time to himself or someone else; but he has to make an arithmetical calculation to determine how much time may elapse before he has to take some action, such as leaving for work or keeping an appointment.
As the users of watches want to know how long to some future event much more often than they want simply to "tell" the time, a conventional display is generally more convenient than a decimal digit readout. To meet this need, several inventors have tried to provide displays for electronic watches which approach the conventional. Some have developed very low power electric motors to move a pair of hands mechanically. Others have used loops of optical display elements to designate angular positions for hours and minutes. Still others have used optical display elements shaped to represent hands and have flashed other optical elements to indicate intermediate times by a time code. Specific examples of the prior art follow.
In U.S. Pat. No. 3,540,209, Keeler and Zatsky show several pseudo-conventional displays using liquid crystal or ferroelectric elements to produce radial line segments for the hour, minute, and second positions. In one embodiment, one set of elements is used as an hour hand to show hour positions and as part of a minute hand showing minute positions. The patent also discusses using the display element characteristics in combination with two level gating.
In U.S. Pat. No. 3,754,392, Daniels uses a ring of 60 light emitting diodes, or LEDs, to display minute and second positions and an inner ring of 12 LEDs to show the hour positions. Daniels applies the hour, minute, and second information to a single decoder in repetitive sequences to energize the appropriate LEDs in short duty cycles.
In apparatus disclosed in U.S. Pat. No. 3,969,887, Fukumoto uses LCDs to show the hour position on one of twelve inner elements and the minute position by cumulatively turning on elements in an outer ring of 60. The minute indication is then a series of elements from the 12 o'clock position to the minute position. Fukumoto uses various front and back conductive segment patterns in combination to minimize the number of connections necessary from the display drivers. Fukumoto connects electrodes together in sets without crossovers by means of meandering leads.
In U.S. Pat. No. 3,823,547, Feldman shows 12 hour elements in the shape of hour hands and 12 elements partially encasing the hour elements so that the combinations appear as minute hands. The 12 hour and minute hand positions show the time within 5 minutes and additional interpolation elements are used to indicate each minute.
In U.S. Pat. No. 3,844,105, Kashio uses two rings of 60 elongated liquid crystal elements to show 60 hour and 60 minute positions. A turned-on element in the inner ring shows the hour position while turned-on elements at the same position in the inner and outer rings show the minute position.
In U.S. Pat. Nos. 3,919,835 and 3,992,875, Kashio uses rings of 12 and 60 elements to show 12 hour positions and 60 minute positions. Electrodes of hour and minute elements are connected together in groups to reduce the connections required to the integrated circuit.
U.S. Pat. No. 3,955,354 to Kiley and Schweitzer utilizes 60 elements to show hour, minute and second positions. The element for the hour position is held on steadily while that for the minute position flashes once per second.
U.S. Pat. No. 3,922,847 to Culley and Kehren incorporates rings of 12 and 60 LEDs to show 12 hour and 60 minute positions. The LED electrodes are connected to groups to minimize the number of pinouts required from the integrated circuit.
U.S. Pat. No. 3,968,639 to Berets et al features 12 elongated elements for showing hour positions and a continuous circumferential band for showing minute positions. The voltage applied to the band is increased to turn on successively longer portions from the 12 o'clock position until, by the end of the hour, the whole band is turned on. The band is then erased for the start of the next hour.
U.S. Pat. No. 3,958,409 to Mamber discloses two sets of 12 LEDs to show the hour and five minute positions with extra LEDs flashing to indicate the number of minutes past the five minute position.
U.S. Pat. No. 3,908,355 to Wiesner discloses conductive elements for hour and minute hands on two different plates in an effort to simulate the passage of one hand over the other.
Two prior art references, Keeler and Zatsky and Kashio, show 60 hour elements and 60 minute elements with an hour and minute element used in combination to represent the minute band. The width available for each of the 60 elements decreases with extension inward from the outer circumference, with the result that the elements must be either very short or very narrow. If too short, they are not effective as hands; if too narrow, they cannot be clearly distinguished and are not effective at all.
Feldman of reference shows 12 hour elements and 12 minute elements with an hour and minute element used in combination for a minute hand. Since the 12 minute hand positions can show the time only to the nearest five minutes, Feldman uses other elements to show individual minutes. Auxiliary elements to show minutes represents a major departure from conventional time displays.